A Multimedia Broadcast/Multicast Service (MBMS) provides a multimedia broadcast/multicast service for a user in a radio cell. In a Long Term Evolution (LTE) system, an MBMS can be provided at both a frequency layer specific to the MBMS and a frequency layer shared with a non-MBMS service. An LTE cell supporting an MBMS can be an MBMS-specific cell or an MBMS and unicast hybrid cell. An MBMS can be transmitted in a single cell or in a plurality of cells. Multi-cell transmission of an MBMS needs to support a Multimedia Broadcast multicast service Single Frequency Network (MBSFN) transmission mode.
The MBSFN transmission mode refers to synchronous transmission in a plurality of cells at the same frequency at the same time. The use of this transmission mode can save a frequency resource and improve a spectrum utilization ratio. It requires the plurality of cells to transmit the same content at the same time, thus a User Equipment (UE) can regard the plurality of MBSFN cells as a large cell. Therefore, the UE cannot be subject to interference of a signal from an adjacent cell but can benefit from superposition of signals from the plurality of MBSFN cells. Both the MBMS-specific cell and the MBMS and unicast hybrid cell can adopt the MBSFN transmission mode. Moreover, if an advanced UE receiver technology is utilized, the problem of a time difference in multi-path propagation can be addressed, to eliminate intra-cell interference. A diversity effect resulting from such multi-cell transmission at the same frequency can further address the problem of coverage of a dead zone, to enhance the reliability of reception and improve a coverage ratio.
MBMS multi-cell transmission have the follow technical features:
There is synchronous transmission of an MBMS in an MBSFN area;
Integration of multi-cell MBMS transmission is supported;
Logic channels, i.e., a Multicast Traffic Channel (MTCH) and a Multicast Control Channel (MCCH), are mapped to a transmission channel for Point to Multipoint (PTM) transmission, i.e., a Multicast Channel (MCH) and further to a Physical Channel, i.e., a Physical Multicast Channel (PMCH);
The MBSFN synchronization area can be configured semi-statically, for example, by Operation & Maintenance (O&M); and
A first 1 to 2 symbols in an MBSFN sub-frame are control symbols bearing a PDCCH for unicast transmission scheduling, and following symbols are a data field bearing the PMCH when there is an MBMS to be transmitted.
Logic channels related to MBMS transmission generally include a Broadcast Control Channel (BCCH), the MCCH and the MTCH.
The respective channels generally have the following functions.
The Broadcast Control Channel (BCCH) is for the network to broadcast system information to the UE. For the MBMS, there are two parts of a broadcast message to be transmitted:
All of MBSFN sub-frames indicated in a System Information Block (SIB) 2; and
An SIB13 schedules notification sub-frame (a notification mechanism for an MCCH change notification) and the MCCH, where the scheduling command is used to indicate for an MBSFN sub-frame for transmitting the notification and the MCCH.
The Multicast Control Channel (MCCH) is a point to multipoint downlink channel for the network to transmit MBMS related control information in the MBSFN area to the UE, where an MCCH can correspond to one or more MTCHs (that is, can carry control information of a plurality of MTCHs). The MCCH can include sub-frame assignment of the MBSFN area, configuration information of the PMCH (or MCH), etc., where the configuration information of the PMCH (or MCH) includes, for example, MBMS session information, data Modulation and Coding Scheme (MCS) configuration, a PMCH sub-frame location and a scheduling period.
The Multicast Traffic Channel (MTCH) is a point to multipoint downlink channel for the network to transmit MBMS data to the UE.
The network indicates the configuration information of the MCCH to the UE over the BCCH (including the SIB2 and the SIB13) and further provides the UE with the PMCH or MCH information over the MCCH, and the UE reads MCH Scheduling Information (MSI) of the specific service over the PMCH or the MCH and thereby can receive the MBMS over the MTCH. An MBSFN sub-frame for transmission of the MBMS is finally indicated by an MCH Scheduling Information Media Access Control (MAC) Control Element (MSI MAC CE).
FIG. 1 illustrates a relationship between an MBMS service area and MBSFN synchronization areas, etc.
As specified in the physical layer protocol, a UE of an LTE Release 10 (RIO) system can receive data transmitted over a Physical Downlink Shared Channel (PDSCH) in an MBSFN sub-frame. Specifically, only a UE configured with the transmission mode 9 (tm9) by an evolved NodeB (eNB) can receive data, including downlink transmission data of Semi-Persistent Scheduling (SPS), transmitted over a PDSCH in an MBSFN sub-frame.
The semi-persistent scheduling transmission has a characterization that an Evolved NodeB (eNB) notifies a UE of information of a semi-persistent scheduling resource assigned for the UE, including a time-frequency resource, a transmission format (e.g., a modulation and coding scheme, etc.), etc., in a scheduling command transmitted over a Physical Downlink Control Channel (PDCCH), and starting from an assigned sub-frame of the semi-persistent scheduling resource, time-frequency resource locations corresponding to subsequent sub-frames spaced at a fixed interval are reserved for the UE to transmit data in the specified transmission format without being further instructed by a PDCCH command, and such semi-persistent scheduling transmission without a scheduling command is also referred to as configured downlink (DL) assignment. Semi-persistent scheduling transmission will not be terminated until the eNB transmits a PDCCH command to release the SPS resources. Referring to FIG. 2, downlink semi-persistent scheduling transmission will be described below as an example.
At a moment of time T1, the eNB transmits a PDCCH command to assign an SPS resource and the first downlink SPS transmission data at the moment of time T1, where information of the SPS time-frequency resource and a transmission format is carried over the PDCCH;
At moments of time T2 to T4, the UE receives the SPS transmission data in the specified transmission format over the specified time-frequency resource in sub-frames spaced at a fixed interval (T), and no further PDCCH command is required for scheduling in these sub-frames, that is, the SPS resources at the moments of time T2 to T4 are pre-configured downlink resources, and such downlink transmission is so-called configured DL assignment; and
At a moment of time T5, the eNB transmits PDCCH information to instruct the UE to release the SPS resource so that the UE is instructed to release the originally assigned SPS resource, to terminate the SPS transmission.
However, the existing higher-layer protocol does not support reception of the SPS transmission data by the UE in an MBSFN sub-frame, therefore, the semi-persistent scheduling transmission cannot be implemented in the MBSFN sub-frame in the prior art.